Comparing The Records
The δ18O record of air (in the Vostok ice core) and marine sediments has been compared with estimates of solar insolation, which should affect both temperature and ice volume. Nicholas Shackleton orbitally tuned the Antarctic ice core air δ18O (i.e. he matched the signal to this assumed forcing), and used spectral analysis to identify and subtract the component of the record that in this interpretation could be attributed to a linear (directly proportional) response to the orbital forcing. The residual signal (the remainder), when compared with the residual from a similarly retuned marine core isotope record, allowed him to estimate the proportion of the signal that was attributable to ice volume, with the rest (having attempted to allow for the Dole effect) being attributed to temperature changes in the deep water.
The 100,000-year component of ice volume variation was found to match sea level records based on coral age determinations, and to lag orbital eccentricity by several thousand years, as would be expected if orbital eccentricity were the pacing mechanism. Strong non-linear "jumps" in the record appear at deglaciations, although the 100,000-year periodicity was not the strongest periodicity in this "pure" ice volume record. The separate deep sea temperature record was found to vary directly in phase with orbital eccentricity, as did Antarctic temperature and CO2; so eccentricity appears to exert a geologically immediate effect on air temperatures, deep sea temperatures, and atmospheric carbon dioxide concentrations. Shackleton concluded: "The effect of orbital eccentricity probably enters the paleoclimatic record through an influence on the concentration of atmospheric CO2". The mechanism causing these cyclic temperature changes remains at the heart of the 100,000-year problem.
Read more about this topic: 100,000-year Problem
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